1. Field of the Invention
The present invention relates to a power supply device that includes a number of battery cells, which are arranged side by side, and in particular to a power supply device that can supply electric power to an electric motor for vehicle traveling, a power supply device that can be charged with electric power generated by natural power sources such as solar batteries or with midnight electric power, a power supply device suitable as blackout backup power supplies that are suitably prepared for a blackout, and a vehicle that includes the power supply device.
2. Description of the Related Art
A power supply device required to provide a large amount of output power includes a number of batteries that are connected in series or in parallel to each other for increasing its output power. For example, a plurality of rectangular battery cells are arranged side by side in an exterior case (see Japanese Patent Laid-Open Publication No. JP 2009-170,258 A) such as in a power supply device for vehicles such as an electric vehicle that is driven by an electric motor and a hybrid car that is drive both by an electric motor and an internal-combustion engine, a power supply device that can be charged by natural power sources, a power supply device that can be suitably prepared for a blackout, or the like. In this power supply device, as shown in FIG. 34, a number of rectangular battery cells 101 are arranged side by side, and compose a battery block 110. The rectangular battery cell 101 includes positive/negative electrode terminals 113 that are arranged on the upper surface of the upper surface of a rectangular exterior container 111, as shown in FIG. 35. In the case where the electrode terminals 113 of the rectangular battery cells 101 are serially connected to each other in the battery block 110, the output voltage of the battery block 110 can be high.
In the case where the exterior container 111 is formed of a metal such as aluminum, the rectangular battery cell 101 can be thin and have high stiffness. Lithium-ion rechargeable batteries or nickel metal hydride batteries can be used as the rectangular battery cells. In the case of lithium ion batteries, the exterior container is not connected to the electrodes. Accordingly, a potential on the exterior container will be an intermediate potential between the positive/negative electrode terminals. In the case of nickel metal hydride batteries, the exterior container is connected to one of the positive/negative electrodes. Accordingly, a potential on the exterior container is the same as the electrode that is connected to the exterior container. For this reason, when these rectangular battery cells are arranged side by side so that the battery cells adjacent to each other are serially connected to each other, potential difference will be provided between the exterior containers of the adjacent batteries. When these rectangular battery cells are arranged side by side and serially connected to each other, in order to prevent a short circuit current from flowing through the exterior containers of the batteries, it is necessary to electrically insulate the adjacent batteries from each other. In addition, in order to prevent leakage of current, it is necessary to electrically insulate the rectangular battery cells, which are arranged side by side, from the ground. In order to achieve this, in the case where the battery block includes the rectangular battery cells that are arranged side by side, the exterior containers are electrically insulated from each other. In order to electrically insulate the exterior containers from each other, an electrically insulating separator is sandwiched between the rectangular battery cells. In addition, the surfaces of the exterior container are covered by an electrically insulating sheet. In the case where, the surfaces of the exterior container of the rectangular battery cell are covered by the electrically insulating sheet, it is possible to prevent leakage of current that is caused with water condensed on the surface of the exterior container.
Power supply devices are used in various external environments. For this reason, water may be condensed on the surfaces of power supply devices in some cases. If water is condensed on the surface of the exterior container, the condensed water may cause leakage of current and short circuit current. The reason is that current may flow through the condensed water from one exterior container to another exterior container adjacent to this one exterior container, or current may flow through the condensed water from the exterior container to the ground line, and cause leakage of current. This problem can be prevented by covering the exterior container with the electrically insulating sheet. In particular, if water is condensed on the exterior container, the water will flow downward along the surface of the exterior container. For this reason, it is important to more reliably make the bottom of the exterior container watertight by covering the bottom of the exterior container with the electrically insulating sheet.
In addition, the battery block is placed on and fastened to a bottom plate of the exterior case, which is formed by the working of metal. Alternatively, the battery block is placed on and fastened to a metal cooling plate. Accordingly, if the bottom surface of the exterior container comes in contact with the exterior case or the cooling plate, the problem will arise that short current flows from the rectangular battery cell, or leakage of current occurs.
In order to electrically insulate the exterior container of the rectangular battery cell, in a conventional power supply device shown in FIGS. 36A-36C, the exterior container is inserted into a bag-shaped heat contraction sheet 102 that has a closed bottom so that a bottom surface 111B and the periphery of the exterior container 111 are covered. Specifically, a tube-shaped heat contraction sheet having upper and lower opened ends is divided by cutting into the heat contraction sheets 102, which have a certain length. As shown in FIG. 37, the rectangular battery cell 101 is inserted into the heat contraction sheet 102. Subsequently, the opposed end parts of the heat contraction sheet 102 are welded on the rectangular battery cell 101 bottom surface 111B side by heat as shown in FIGS. 38A and 38B. After that, the heat contraction sheet 211A is shrink-fitted over the battery cell 36. Thus, the heat contraction sheet 102 is brought in tight contact with surfaces of the exterior container 111 as shown in FIGS. 36A-36C.
In this case, as shown in the cross-sectional view of FIG. 36C, the welded part 102x protrudes from the bottom surface 111B of the rectangular battery cell 101. In the case where the welded part 102x protrudes from the bottom surface 111B, the thermal resistivity will increase between the rectangular battery cell 101 and the cooling plate (not shown). Accordingly, the thermally connected state will be poor. In addition, the alignment of the bottom surfaces 111B of the rectangular battery cells 101 will be uneven. As a result, there is a problem that will be difficult to hold the rectangular battery cells 101 on the same plane. On the other hand, since the welded part protrudes from the bottom surface of the rectangular battery cell, the welded part will be likely damaged by the weight of the battery block, or vibration. As a result, in the case where the battery block is placed on and is fastened to the bottom plate of the exterior case or the cooling plate, the damage on the heat contraction sheet may cause leakage of current or short circuit.
Although not illustrated, it is conceivable that the welded part, which protrudes from the bottom surface, is arranged in a gap between the separators adjacent to each other. In the thus-constructed battery block, the exterior container may not be directly thermally connected to the cooling plate, which in turn may reduce cooling effect.
In this case, since a particular part of the bottom of the exterior container is locally supported by the separator, there is a problem that this part in contact with the separator may be likely to be damaged. The reason is that the weight per area of the part in contact with the separator is increased.
The present invention is aimed at solving the problems in the conventional power supply devices. It is a main object of the present invention to provide a power supply device that can prevent a welded part from protruding from the bottom surface of a rectangular battery cell whereby stably fixedly arranging the rectangular battery cells on an exterior case or a cooling plate in proper positions, and can reliably cover the bottom surface of the rectangular battery cell with an electrically insulating film whereby effectively preventing short circuit between exterior containers of the rectangular battery cell adjacent to each other and leakage of current, and to provide a vehicle including this power supply device.